Show links to archive pages based on custom field values in WordPress

I would recommend using a custom taxonomy for this, not a custom field. You can sort and list archives based on a taxonomy far more easily than by custom fields.

However, if you want to list based on the custom field, you're going to need to modify the arguments sent to query_posts() on your archive page to pass in the meta_key and meta_value you're searching by.

To add your query variable:

add_action('init', 'add_custom_meta_url');
function add_custom_meta_url() { global $wp,$wp_rewrite; $wp->
add_query_var('location'); $wp_rewrite->
add_rule('location/([^/]+)','index.php?location=$matches[1]',op'); $wp_rewrite->
flush_rules(false); // This should really be done in a plugin activation
}

Then, your permalinks for the archive will become something along the lines of http://mycoollocationsite.com/location/england http://mycoollocationsite.com/location/ireland http://mycoollocationsite.com/location/usa ... etc ...

Next, you'll need to add whatever value was passed in to your location to the actual query:

add_action('parse_query', 'apply_custom_meta_to_query');
function apply_custom_meta_to_query(&$query) { if (isset($query->
query['location'])) { $query->
query_vars['meta_key'] = 'location'; $query->
query_vars['meta_value'] = $query->
query['location']; unset($query->
query_vars['location']); // You don need this }
}

I'm assuming you're storing your custom data in a field called location ... so change that if I'm wrong.

But this will allow you to filter your archives based on a specific location. If you want to enable date-based archives with this as well that will require some additional rules in my first code block (rightw, this would display a list of all posts with a location meta_key).

Still, I recommend using a custom taxonomy instead. It's cleaner, more extensible, and requires less custom coding. This is also exactly the situation for which custom taxonomies were created ... so please, don reinvent the wheel ...